Olefin polymerization processes and products thereof

ABSTRACT

A novel loop/slurry olefin polymerization process is provided which produces ultra high molecular weight ethylene homopolymers and ultra high molecular weight ethylene copolymers. Catalyst systems used are selected from the group consisting of inorganic oxide supported titanium-containing catalyst systems, inorganic oxide supported organo-zirconium catalyst systems and inorganic oxide supported organo-hafnium catalyst systems.

BACKGROUND

[0001] This invention relates to olefin polymerization processes and theresultant polymer products.

[0002] Ultra high molecular weight olefin polymers such as polyethyleneusually have excellent properties, such as, for example, high impactstrength and dimensional stability, low coefficient of friction,self-lubricating and are highly resistant to most chemicals. Thus,ultrahigh molecular weight polyethylenes are useful in many demandingand extremely critical applications, such as human joint replacements,gears, bullet proof vests, skis, and other applications. However,ultrahigh molecular weight polyethylenes can be difficult to processwith conventional equipment. Since ultra high molecular weight polymercannot be pelletized after leaving the reactor, the polymer must be soldas a fluff or a powder. Therefore, particle size and toughness of theresultant polymer is critical.

[0003] Many commercial methods are available to produce olefin polymers,such as polyethylene. One of the most economical routes to mostcommercial grades of olefin polymers is a loop/slurry process with aparaffin diluent wherein the polymerization process can be carried outat a temperature low enough that the resulting polymer is largelyinsoluble in the diluent. It is believed that commercially acceptableultra high molecular weight ethylene polymers traditionally are madeusing a stirred tank process, in a heavy hydrocarbon diluent.

SUMMARY OF THE INVENTION

[0004] It is an object of this invention to provide very tough ultrahigh molecular weight homopolymers of ethylene and copolymers ofethylene/1-hexene.

[0005] It is another object of this invention to provide ultra highmolecular weight ethylene/1-hexene copolymers having improved physicalproperties compared to conventional ultra high molecular weight ethylenehomopolymers.

[0006] It is a further object of this invention to provide an improvedolefin polymerization process which can produce both homopolymers ofethylene and copolymers of ethylene and at least one other higheralpha-olefin comonomer.

[0007] It is yet another object of this invention to provide an improvedpolymerization process for preparing ultra high molecular weightpolyethylene.

[0008] It is a further object of this invention to provide an improvedolefin polymerization process which can produce copolymers of ethyleneand at least one other higher alpha-olefin comonomer using a catalystsystem selected from the group comprising supported Ziegler-Nattacatalyst systems, organo-zirconium catalyst systems and organo-hafniumcatalyst systems.

[0009] It is a further object of this invention to provide an improvedolefin polymerization process which can produce homopolymers of ethyleneusing a catalyst system selected from the group comprisingorgano-zirconium catalyst systems and organo-hafnium catalyst systems.

[0010] In accordance with one embodiment of this invention, a process isprovided which comprises polymerizing ethylene in a loop/slurry processusing a catalyst system selected from the group comprising supportedZiegler-Natta catalyst systems, organo-zirconium catalyst systems andorgano-hafnium catalyst systems to produce very tough ultra highmolecular weight copolymers of ethylene and at least one other higheralpha-olefin comonomer.

[0011] In accordance with another embodiment of this invention, aprocess is provided which comprises polymerizing ethylene in aloop/slurry process using a catalyst system selected from the groupcomprising supported organo-zirconium catalyst systems andorgano-hafnium catalyst systems to produce very tough ultra highmolecular weight homopolymers of ethylene.

[0012] In accordance with still another embodiment of this invention, aprocess is provided which consists essentially of polymerizing ethylenein a loop/slurry process using a catalyst system selected from the groupcomprising supported Ziegler-Natta catalyst systems, organo-zirconiumcatalyst systems and organo-hafnium catalyst systems to produce verytough ultra high molecular weight copolymers of ethylene and at leastone other higher alpha-olefin comonomer.

[0013] In accordance with still another embodiment of this invention, aprocess is provided which consists essentially of polymerizing ethylenein a loop/slurry process using a catalyst system selected from the groupcomprising supported organo-zirconium catalyst systems andorgano-hafnium catalyst systems to produce very tough ultra highmolecular weight homopolymers of ethylene.

[0014] In accordance with yet another embodiment of this invention, acomposition comprising a very tough, ultra high molecular weightpolyethylene is provided.

DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows three (3) molecular weight distributions obtainedfrom size exclusion chromatography (SEC) of three different polyethylenesamples. “UHMWPE” designates ultra high molecular weight polyethylene.The x-axis, labeled “LOG M”, is the log of the polyethylene molecularweight. The y-axis, labeled “DW/D(LOG M)”, is the differential massfraction. Two curves, designated as “Supported Titanium CatalystSystem”and “Organo-zirconium Catalyst System”, are curves ofethylene/1-hexene copolymers prepared in accordance with the novel,inventive process. The third curve, designated as “Commercial Sample,”is a commercially available polyethylene, GUR 4150 made by HoechstCelanese USA.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] As used in this disclosure, the term “polymer” includes bothhomopolymers and copolymers, even though the terms “homopolymer” and“copolymer” are used in the specification. However, the specific term“homopolymer” means a polymer that is produced from predominantly oneolefin monomer, such as, for example, ethylene. The specific term“copolymer” means a polymer that is produced from predominantly oneolefin and another higher alpha-olefin, such as for example, copolymersof ethylene and butene, ethylene and hexene, ethylene and octene.

Catalyst System

[0017] Three types of catalyst systems can be used in accordance withthis invention to produce ultra-high molecular weight polymers. Thefirst type of catalyst system useful in this invention is an inorganicoxide-supported titanium-containing catalyst system, commonly referredto as “Ziegler-Natta” catalysts. As used in this disclosure, the term“support” refers to a carrier for another catalytic component. However,by no means, is a support an inert material; it is possible that asupport can contribute to catalytic activity and selectivity.Commercially available titanium catalyst systems typically comprisecomplexes of titanium halides with organometallic compounds, such asaluminum alkyls. Exemplary magnesium/titanium catalyst systems include,but are not limited to, those disclosed in U.S. Pat. Nos. 4,394,291;4,326,988; and 4,347,158, herein incorporated by reference. Exemplaryinorganic oxide catalyst system supports include, but are not limitedto, either alone or in combination, inorganic oxides of silica, aluminaand/or titania, phosphated inorganic oxides, and mixtures thereof.Particularly preferred supports for the titanium-type catalyst systemare selected from the group consisting of silica, silica-alumina,alumina, fluorided alumina, silated alumina, thoria, aluminophosphate,aluminum phosphate, phosphated silica, phosphated alumina,silica-titania, coprecipitated silica/titania, fluorided/silatedalumina, and mixtures thereof. Preferably, the titanium-type catalystsystem support comprises silica, titania, and alumina, either alone orin combination and either modified or unmodified.

[0018] The two other types of catalyst systems useful in the presentinvention are selected from the group consisting of organo-zirconium andorgano-hafnium catalyst systems which have beta-stable ligand(s). Theorgano-zirconium and organo-hafnium catalyst systems must be supportedon an aluminum-containing support.

[0019] The organo-zirconium and organo-hafnium catalyst systems comprisea supported, beta(β)-stabilized Group IVB (Chemical Abstracts Serviceversion of the Periodic Table) compound. Alkyl compounds of Group IVBmetals can readily eliminate a hydrogen through a mechanism referred toas beta-hydride elimination, shown below in Equation 1.

[0020] wherein α=alpha, β=beta, γ=gamma

[0021] Beta-stabilized compounds are inherently more stable then thosecompounds which contain β-hydrogens. During an elimination reaction, aβ-hydrogen on the ligand is transferred to the metal and an alkenecompound is eliminated. One way to deter this elimination reaction is touse ligands that have no β-hydrogens. Exemplary β-stabilized compoundscan have a general formula of CH₂X(R)₃, wherein X is selected from thegroup consisting of carbon, silicon, germanium, tin and lead and whereinR can be the same or different and is selected from the group consistingof saturated or unsaturated hydrocarbons. Preferably, R is selected fromthe group consisting of alkyl radicals of from about 4 to about 12carbon atoms, alicyclic radicals of from about 4 to about 12 carbonatoms, aryl radicals of from about 6 to about 24 carbon atoms andhydrocarbyl substituted aryl radicals such as alkylaryl andcycloalkylaryl of from about 6 to about 24 carbon atoms. Exemplarycompounds having a general formula of MR₄ wherein M is selected from thegroup consisting of titanium, zirconium and hafnium and R can be thesame or different and is selected from the group consisting of—CH₂C(CH₃)₃,-benzyl, and —CH₂SiMe₃. Exemplary beta stable ligandsinclude, but are not limited to, benzyl, trimethylsilylmethyl (TMSM),1-methylene-1-naphthyl and neopentyl.

[0022] Zirconium or hafnium usually is present in the catalyst system inan amount within a range of about 0.01 to about 6 weight percent,preferably within a range of about 0.1 to about 5 weight percent, basedon the total mass of the catalyst system (support plus zirconium orhafnium metal). Most preferably, zirconium or hafnium is present in thecatalyst system in an amount within a range of 0.2 to 4 weight percentbased on the total mass of the catalyst system for best catalyst systemactivity and productivity, as well as best polymer product particlesize.

[0023] Any aluminum-containing support useful to supportorgano-zirconium and organo-hafnium catalyst systems can be used.Exemplary catalyst supports include, but are not limited to, inorganicoxides, either alone or in combination, and mixtures thereof. As statedearlier, the support must contain aluminum. Exemplary supports for theorgano-zirconium and organo-hafnium catalyst systems are selected fromthe group consisting of alumina (Al₂O₃), flourided alumina, silatedalumina, flourided/silated alumina, aluminophosphate, aluminumphosphate, phosphated alumina, silica/alumina, and mixtures of two ormore thereof. Preferred supports are selected from the group consistingof alumina, aluminophosphate and silica alumina. Most preferably, anygrade or designation or type of alumina, with a minor amount of silica,preferably, less than 10 weight percent, most preferably, less than 6weight percent, is used as a catalyst system support for best resultantcatalyst system activity.

[0024] Supports with high pore volume and high surface area arepreferred. Alumina supports having higher surface areas and porevolumes, used in accordance with this invention, can result in catalystsystems having higher catalyst system activity and productivity.Generally, aluminum-containing supports useful in this invention have asurface area of greater or equal to about 150 m²/gram, preferablygreater than about 200 m²/gram, and a pore volume of greater than orequal to about 0.7 cc/g, preferably greater than about 1.5 cc/g. Mostpreferably, aluminum-containing supports useful in this invention have asurface area within a range of 300 to 600 m²/gram and a pore volumewithin a range of 1.8 to 4 cc/g.

[0025] The particle size of the polymer fluff is critical. In accordancewith this invention, it has been found that a correct selection ofparticle size of the catalyst system particles can control the particlesize of the resultant polymer fluff. Usually, supported catalyst systemparticles are within a range of about 1 to about 40 microns, preferablywithin a range of about 2 to about 20 microns. Most preferably, in orderto have a correctly sized polymer product, catalyst particles are keptwithin a size range of about 4 to about 16 microns.

[0026] Preferably, a cocatalyst, such as, for example, aluminum alkyland/or boron alkyl compounds, is not used during polymerization with theorgano-zirconium or organo-hafnium catalyst systems. The presence ofthese common cocatalysts does not appear to enhance catalyst systemactivity or productivity and can, in fact, reduce catalyst systemactivity and productivity.

Reactants

[0027] The polymers produced in accordance with the process of thisinvention are homopolymers of ethylene and copolymers of ethylene andhigher alpha-olefin comonomers. The present invention is unique in thatcopolymers of ethylene and higher alpha-olefin comonomers have ultrahigh molecular weight. Preferably, the ethylene concentration in thepolymerization reactor is within a range of from about 2 weight percentto about 20 weight percent, based on the total liquid contents of thereactor. Most preferably, the ethylene concentration in thepolymerization reactor is within a range of from about 4 to about 15weight percent. Measured in another manner, ethylene concentration inthe polymerization reactor flash gas is within a range of from about 5weight percent to about 12 weight percent. Most preferably, the ethyleneconcentration in the polymerization reactor flash gas is within a rangeof from about 6.5 to about 10 weight percent. While ethyleneconcentration does not significantly affect the molecular weight of theresultant polymer, higher or lower ethylene concentration can effectcatalyst activity.

[0028] The alpha-olefin comonomers used in the present invention must beselected from the group consisting of 1-butene, 1-hexene, and mixturesthereof in order to produce a copolymer with desirable properties aswell as ease of use in a loop/slurry polymerization reaction process.The most preferred comonomer is 1-hexene to produce a copolymer with thebest product properties. If a comonomer is present duringpolymerization, the comonomer concentration in the polymerizationreactor is within a range of from about 0.5 to about 20 mole percent.Most preferably, comonomer is present within a range of about 1 to about15 weight percent.

Polymerization Process

[0029] Polymerization of the olefin monomer(s) must be carried out underloop/slurry polymerization conditions wherein the temperature is keptbelow the temperature at which polymer swells. Such polymerizationtechniques are well known in the art and are disclosed, for instance, inNorwood, U.S. Pat. No. 3,248,179, the disclosure of which is hereinincorporated by reference. A light diluent, loop polymerization processis much more preferred than a stirred tank reactor because a stirredtank cannot contain isobutane, which is necessary to produce othercommercially popular high density polyethylene polymer product grades. Aloop reactor also has an advantage in that isobutane diluent can beflashed off in a loop process, eliminating the necessity of separatingpolymer product from solvent. Additionally, the greater heat transfersurface of a loop reactor offers much more versatility for plantoperation, and often less polymer swelling during polymerization.

[0030] The temperature of the polymerization reactor, or reaction zone,according to this invention, is critical and is dependant on the type ofcatalyst system employed. Polymerization reaction temperatures with aZiegler-Natta catalyst system must be kept within a range of about 150°F. to about 180° F. (65° C. to 83° C.), preferably within a range ofabout 160° F. to about 170° F. (71° C. to 77° C.). Most preferably, thereaction zone temperature is within a range of 162° F. to 168° F. (72°C. to 76° C.). Polymerization reaction temperatures with a zirconium- orhafnium-containing catalyst system must be kept within a range of about158° F. to about 212° F. (70° C. to 100° C.), preferably within a rangeof about 167° F. to about 203° F. (75° C. to 95° C.). Most preferably,the reaction zone temperature is within a range of 176° F. to 194° F.(80° C. to 90° C.). The temperature range is critical in order toproduce an ultra high molecular weight polyethylene. Too high of areactor temperature can produce a polymer with too low of a molecularweight; too low of a reactor temperature can make the polymerizationprocess inoperable because a lower reactor temperature can be difficultto maintain due to the exothermic polymerization reaction, flashing offreactor diluent can be difficult, and can produce a polymer with acommercially unacceptable molecular weight.

[0031] The loop/slurry process used in this invention must be carriedout in an inert, light hydrocarbon diluent (medium), selected from thegroup consisting of hydrocarbons having three or four carbon atoms permolecule. Exemplary diluents include, but are not limited to propane,n-butane, isobutane, and mixtures thereof. Diluents having greater orless than three or four carbon atoms per molecule can be difficult toseparate from the polymer product during the polymer recovery process.Isobutane is the most preferred diluent due to low cost and ease of use.

[0032] Pressures in the loop/slurry process can vary from about 110 toabout 1000 psig (0.76-4.8 MPa) or higher, preferably 350 to 600 psig.The catalyst system is kept in suspension and is contacted with ethyleneat a sufficient pressure to maintain the medium and at least a portionof the ethylene in a liquid phase. The reactor medium and temperaturethus are selected such that the polymer is produced and recovered assolid particles. Catalyst system concentrations in the reactor can besuch that the catalyst system content ranges from 0.0001 to about 0.1weight percent based, on the weight of the reactor contents.

[0033] Hydrogen never is added to the polymerization reactor becausehydrogen has too great of an effect on the molecular weight of theresultant polymer.

Products

[0034] Polymers produced in accordance with this invention arehomopolymers of ethylene and copolymers of ethylene and higheralpha-olefin comonomers. Polymers produced according to this inventionhave an ultra high weight average (M_(w)) molecular weight, generallyabove one million (1,000,000). Preferably, polymers produced inaccordance with this invention have a molecular weight within a range ofgreater than about two million (2,000,000) and most preferably, within arange of greater than or equal to about 3,000,000 up to about10,000,000.

[0035] Comonomer incorporation into the inventive copolymers usually iswithin a range of about 0.05 to about 10 weight percent comonomer,preferably within a range of about 0.07 to about 5 weight percent.Preferably, comonomer is present in the copolymer within a range of 0.15to 2 weight percent for best resultant copolymer properties. Expressedin different terms, the inventive copolymers usually comprise comonomerwithin a range of about 0.015 to about 3.5 mole percent comonomer,preferably within a range of about 0.023 to about 1.7 weight percent.Preferably, comonomer is present in the copolymer within a range of 0.5to 0.7 weight percent for best resultant copolymer properties.

[0036] Since the molecular weight of these polymers is so high, thepolymers will exhibit a value of zero (0) for both the melt index (MI)and high load melt index (HLMI). The inherent viscosity (IV) of thepolymers generally is greater than about 19, preferably within a rangeof about 20 to about 30.

[0037] Most preferably, the polymers will have an IV within a range of22 to 28.

[0038] The density of these novel polymers usually is within a range ofabout 0.91 g/cc to about 0.95 g/cc, preferably from about 0.92 to about0.94 g/cc. Most preferably, the polymer density is within a range ofabout 0.925 to about 0.935 g/cc.

[0039] Another critical, defining physical characteristic of thesepolymers is the fluff, or powder, particle size. Usually, the particlesize is less than about 400 microns (40 mesh), preferably within a rangeof about 400 microns to about 40 microns (300 mesh). Most preferably,the particle size is within a range of about 50 to about 400 microns.Particle sizes of larger that about 400 microns often can appear in thefinished product as a flaw, or a white patch. While not wishing to bebound by theory, it is believed that this defect appears because theparticles are not molded by typical methods in the art, but are merelyfused together by compression. Fine, or small, particles can inhibittransport of the powder through conveyor blowers because the fineparticles can cling to walls by static and can plug downstream filtersdue to blowover.

[0040] Polymers produced according to this invention must be very tough,as evidenced by a sand wheel abrasion test, tensile strength,elongation, flexural modulus, hardness and Izod impact strength. Themost important of these tests is the sand wheel abrasion test wherein aplaque of compression molded polymer is subjected to sanding and theamount of polymer lost is measured. Generally, the compression moldedpolymer sample loss is less than or equal to about 150 grams,preferably, less than about 140 grams. Most preferably, the compressionmolded polymer sample loses between zero (0) and 125 grams.

[0041] Polymer tensile strength at yield is within a range of about 15to about 30 MPa, preferably, within a range of about 19 to about 24 MPa.Most preferably, as an indicator of toughness, the tensile strength atyield is within a range of 20 to 24 MPa. Tensile strength at breakusually is greater or equal to about 30 MPa, preferably greater thanabout 35 MPa. Most preferably, as an indicator of toughness, the tensilestrength at break is greater than 38 and less than 75 MPa.

[0042] Izod impact usually is greater or equal to about 45 kJ/m²,preferably greater than about 50 kJ/m². Most preferably, as anotherindicator of toughness, the Izod impact is within a range of about 55 toabout 200 kJ/m². Izod impact is not only related to the polymer itself,but also is an indicator of how well the polymer particles fuse, orknit, together during the fusion process. Polymers having too high amolecular weight can have poor Izod impact strength because of poorfusion. Thus, Izod impact strength often can go through a maximum asmolecular weight is increased.

[0043] Another critical property of these novel, ultra high molecularweight polymers includes physical appearance, such as cleanliness andwhiteness. High bulk density also is important because bulk density isrelated to the amount of compression of the polymer during fusion. A lowbulk density can inhibit and slow down processing rates. Generally,polymers produced in accordance with this invention have a bulk densityof greater than about 0.1 g/cc, preferably, greater than about 0.15g/cc. Most preferably, polymer bulk density is within a range of 0.25 to1 g/cc.

[0044] A further understanding of the present invention and itsadvantages are provided by reference to the following examples.

EXAMPLES Example 1

[0045] Ethylene homopolymers and copolymers were prepared under batchparticle form process conditions by contacting the catalyst system withethylene and optionally a comonomer in a 2.3 liter, jacketed, benchscale autoclave reactor. Isobutane was the diluent; hydrogen and/orcomonomer were added to the reactor for some of the runs. The reactorwas operated for a time of 60-75 minutes. Reactor temperature was 194°F. (90° C.), unless stated differently, and total reactor pressure(isobutane plus ethylene) was 3.8 MPa (550 psig). Polymer fluff wasremoved from the reactor following polymerization for analysis. Thecatalyst systems used were prepared as described below; some wereprepared in-situ in the reactor and some were prepared external to thereactor. Catalyst systems used in the Examples had an average particlesize of 10 microns. Cocatalyst was not present during polymerization inExample 1.

[0046] Zirconium tetrakis(trimethylsilylmethyl) (Zr(TMSM)₄) and hafniumtetrakis(trimethylsilylmethyl) (Hf(TMSM)₄) were prepared in a mannersimilar to that taught by M. R. Collier, M. F. Lappert and R. Pearce inSilylmethyl and Related Complexes: Part 1. Kinetically Stable Alkyls ofTitanium(IV), Zirconium(IV) and Hafnium (IV); J. C. S. Dalt. Trans (pp.445-451, 1973), herein incorporated by reference, using toluene as acatalyst system preparation reaction solvent. All reagents were handledunder an inert (nitrogen) atmosphere. 1.08 g zirconium(IV)chloride orwas slurried with 96 ml toluene and cooled to −78° C. Then, 4.4 ml of1.0M Li(TMSM) in pentane was added; the solution was kept at −78° C. andstirred for one hour. During the second hour, the solution was stirredand brought to room temperature. A precipitate settled and a faintyellow solution was removed. Assuming 100% reaction, the solution had atheoretical concentration of 1 mg Zr/ml. Hf(TMSM)₄ was prepared in asimilar manner to yield 1 mg Hf/ml.

[0047] Alumina catalyst system supports were either Ketjen-G (Al₂O₃),having a surface area of about 340 m²/gram and a pore volume of about2.1 cc/g, comprises about 0.5 weight percent silica and is commerciallyavailable from Akzo, or SRSII (Al₂O₃), commercially available fromGrace-Davison and which comprises about six (6) weight percent silica.The supports were screened through a 325 mesh (50 μm opening) screen;the smaller particle size fraction (higher screen number) was retainedfor use. After screening, catalyst supports were calcined at 600° C. inair.

[0048] In-situ catalyst systems were prepared by adding 50 to 100 mgscreened and calcined alumina support to the reactor against a countercurrent of isobutane. The reactor was sealed and half the isobutane wasadded; the stirrer was started. The desired organometallic compound wasadded to the reactor with the other half of the isobutane. If used,1-hexene was added concurrently with ethylene. The reactor was broughtto pressure and ethylene was fed on demand. Ethylene concentration inthe reactor in Runs 101-105 was 14 weight percent.

[0049] Externally prepared, supported catalyst systems were made byslurrying 7.7 g of screened, calcined in 50 ml of heptane, followed byaddition of 7.7 ml of a 10 mg Zr/ml solution of Zr(TMSM)₄. The slurrywas stirred for 10 minutes, the solid was recovered and washed twicewith 50 ml heptane. A portion of the slurry was removed and dried at100° C. under a stream of nitrogen to give a free-flowing powder.Polymerization with externally prepared catalyst systems was the same ascatalyst systems prepared in-situ, except that supported catalyst systemwas fed to the reactor in lieu of catalyst support only.

[0050] Polymer product was collected from each run and passed through a40 (U.S.) mesh (400 micron) screen to remove large particles. Sievedsamples were compression molded and tested according to the followingprocedures:

[0051] Density (g/ml): ASTM D 1505-68 and ASTM D 1928, Condition C.Determined on a compression molded sample, cooled at about 15° C. perminute, and conditioned at room temperature for about 40 hours.

[0052] High Load Melt Index (HLMI)(g/10 min): ASTM D1238-95, conditionE, determined at 190° C. with a 21,600 gram weight.

[0053] Bulk Density (lbs/ft³): ASTM D1895-89.

[0054] Tensile Strength ((MPa): ASTM D638-86.

[0055] Elongation (%): ASTM D638-86.

[0056] Izod Impact, notched (kJ/m²): ASTM D256(a)-84.

[0057] Flexural Modulus (MPa): ASTM D790-95a.

[0058] Tensile Impact (kJ/m²): ASTM D1822-89.

[0059] Sand Wheel Abrasion (grams lost, g): ASTM D65-94. Lower valuesare more desirable, as an indication of resistance to abrasion.

[0060] Shore D Hardness: ASTM D2240-86.

[0061] Intrinsic Viscosity (dl/g): Calculated from molecular weightdistribution using Mark-Houwink constants appropriate for polyethylenein 1,2,4-trichlorobenzene. ASTM D4020-92 procedure includes a definitionof ultrahigh molecular weight polymers.

[0062] Molecular Weight Distribution: Molecular weights and molecularweight distributions were obtained using a Waters 150 CV gel permeationchromatograph with trichlorobenzene (TCB) as the solvent, with a flowrate of 1 mL/minute at a temperature of 140° C. BHT(2,6-di-tert-butyl-4-methylphenol) at a concentration of 1.0 g/L wasused as a stabilizer in the TCB. An injection volume of 220 μL was usedwith a nominal polymer concentration of 0.3 g/l (at room temperature).Dissolution of the sample in stabilized TCB was carried out by heatingat 160-170° C. for 20 hours with occasional, gentle agitation. Thecolumn was made using two Waters HT-6E columns (7.8×300 mm). The columnswere calibrated with a broad linear polyethylene standard (PhillipsMarlex® BHB 5003) for which the molecular weight had been determined.

[0063] Polymer properties are given in Table 1. TABLE 1 Run 101 102 103104 105 Catalyst System Zr(TMSM)₄ Zr(TMSM)₄ Zr(TMSM)₄ Zr(TMSM)₄Zr(TMSM)₄ 1-Hexene added (g) 0 20 60 0 60 Reactor Temp., ° C. 90 90 9075 75 Reactor Pressure, psig 550 550 550 375 375 Density (g/cc) 0.9290.930 0.927 0.930 0.927 1-Hexene Content^((a)) N/A 0.07 mole % N/A N/AN/A 0.2 Wt % Tensile Strength (MPa) 45.3 56.5 64.4 65.4 58.8 TensileYield (MPa) 22.8 20.5 19.1 22.4 21.6 Elongation (%) 246 226 290 214 253Sand Wheel Abrasion (g) 64 62 75 75 61 Izod Impact (kJ/m²) 91 91 85 7283 Shore D Hardness 68 67 68 70 69

[0064] The data in Table 1 show that even with the addition of 1-hexene,density drops only very slightly, about 0.002 or 0.003 g/cc. However,the amount of 1-hexene added to Runs 202, 203, and 205, based on typicalloop/slurry operating results, usually is enough to move the density atleast 0.02 or 0.03 g/cc. Second, usually incorporation of 1-hexenealmost always lowers the molecular weight of the resultant polymer.Thus, the copolymers produced in Runs 202, 203 and 205 are beingcompared to homopolymers at a higher molecular weight. Nearly all of thepolymer properties (aside from those actually improved by the additionsof 1-hexene) are still quite similar to homopolymers.

[0065] Size exclusion chromatography (SEC) results are shown in FIG. I.The curve designated as “Organo-Zirconium Catalyst System” is the forethylene/1-hexene copolymer product made in Run 103. This sample,analyzed by SEC, had a weight average molecular weight (M_(w)) of about3,820,000, a number average molecular weight (M_(n) of about 915,000 anda calculated IV of about 21.7 dl/g. Note that the curve designated as a“Commercial Sample” had a similar SEC curve as that of the SupportedTitanium Catalyst System sample.

Example 2

[0066] Catalyst systems were prepared as described in Example 1, exceptthat the faint yellow zirconium or hafnium solutions, assuming 100%reaction, had a concentration of 10 mg Zr/ml or 10 mg Hf/ml prior to theaddition of the alumina support. These higher concentration solutionsminimized the actual quantity of catalyst system added to the reactor.Polymerization was carried out in a continuous particle form process bycontacting catalyst system with ethylene, employing a liquid full loopreactor, having a volume of 23 gallons (87 liters), isobutane as thediluent; no hydrogen was added to the reactor during Run 201, 1-Hexenecomonomer was added to Run 202 to have a flash gas concentration of 0.64mole percent (1 weight percent). The reactor was operated to have aresidence time of about 1.25 hrs. The reactor temperature was 194° F.(90° C.) for Run 201 (homopolymer) and 185° F. (85° C.) for Run 202(copolymer), and the pressure was 530 psig. At steady state conditions,the isobutane feed rate was about 51 1/hr, the ethylene feed rate wasabout 23 lbs/hr, with a reactor ethylene concentration of about 16 molepercent. Polymer was removed from the reactor at the rate of 22 lbs/hr.The sieved product was blended with 0.4 weight percent, based on theweight of polymer, calcium stearate (Ca St) by tumbling. All othervariables remained constant. The results are given in Table 2. Particlesize analyses are given in Table 3. TABLE 2 Run 201 (homo- Run 202Commercial Commercial Property polymer) (copolymer) Sample A^((a))Sample B^((b)) Density, g/cc 0.930 0.929 0.932 0.929 1-Hexene N/A 0.24mole % N/A ND content © 0.72 wt % Tensile Strength, 20.4 18.5 22 20.4Yield, MPa Tensile Strength, 61.8 59.3 41.7 39.9 Break, MPa Elongation,% 252 313 287 345 Izod Impact, 76 81 55.3 90.6 kJ/m² Tensile Impact,2910 2940 1890 2400 kJ/m² Flexural 543 509 712 606 Modulus, MPa Flexural650 643 712 606 Strength, MPa Sand Wheel 71 74 106 96 Abrasion

[0067] TABLE 3 Run 201 Run 202 Commercial Commercial Property(homopolymer) (copolymer) Sample A^((a)) Sample B^((b)) >354μ, wt % 0.20.4 0.46 0.49 retained >250μ, wt % 2.0 2.8 56 8.9 retained >177μ, wt %5.2 8.4 30 31.3 retained >105μ, wt % 21.2 34.0 12 45.6 retained <105μ,wt % 71.1 54.4 1 13.8 retained

[0068] The data demonstrate that acceptable homopolymers andethylene/1-hexene copolymers can be produced using organo-zirconiumcatalyst systems and that 1-hexene is incorporated in to the comonomer.

Example 3

[0069] Ethylene copolymers were prepared under continuous particle formprocess conditions similar to Example 1 by contacting the catalystsystem with ethylene and optionally a comonomer in a 1 gallon, jacketed,bench scale autoclave reactor. Isobutane was the diluent; hydrogen wasnot added to the reactor. Comonomer was added to the reactor inquantities shown in Table 4. The reactor was operated for a time of60-75 minutes. Reactor temperature was 140° F. (60° C.) and totalreactor pressure (isobutane plus ethylene) was 3.8 MPa (550 psig). Run301 had 0.0148 g catalyst system and 50 g 1-hexene fed to the reactor;Run 302 had 0.0259 g catalyst system and 100 g 1-hexene fed to thereactor. Polymer fluff was removed from the reactor followingpolymerization for analysis. The catalyst systems used were commerciallyavailable catalyst systems purchased from W. R. Grace and Company, theDavison business unit, designated as Davison Sylopol® 5910, having anaverage particle size of 10 microns. Sales literature for Sylopol® 5910provides a chemical analysis (weight percent) of 15.16% Cl, 4.44% Al,2.95% Mg, 0.60% Ti and a Mg/Ti molar ratio of 9.69. Generally, thecatalyst system is a silica-supported Ziegler-Natta catalyst, alsodescribed as a Ziegler-Natta catalyst deposited on silica. 0.5 ml of a15 weight percent solution of triethylaluminum (TEA) cocatalyst wasadded to the reactor. The results of these runs are given below in Table4. TABLE 4 Run 301 302 Ethylene Conc. (wt %) 0.65 2.0 Density (g/cc)0.926 0.927 Bulk Density (g/cc) 0.36 0.31 Tensile Strength, Yield, MPa22.0 20.3 Tensile Strength, Break, MPa 56.2 46.9 Elongation, % 271 262Izod Impact, kJ/m² 57 75 Shore D Hardness 68 66 Sand Wheel Abrasion 10985 Finer than 200 mesh (wt %) 69.0 29.4 Larger than 35 mesh (wt %) 0.320.9 Activity (ppm Ti) 9.7 2.2

[0070] The data in Table 4 show that a supported titanium-containingcatalyst system can produce ultrahigh molecular weight copolymers ofethylene and 1-hexene.

[0071] Size exclusion chromatography (SEC) results are shown in FIG. I.The curve designated as “Supported Titanium Catalyst System” isexemplary for ethylene/1-hexene copolymer products made in theabove-described bench scale reactor. For the SEC run, reactor pressurewas 250 psig, 0.0564 g catalyst system and 50 g 1-hexene were fed to thereactor. This, sample analyzed by SEC, had a weight average molecularweight (M_(w)) of about 2,640,000, a number average molecular weight(M_(n)) of about 227,000 and a calculated IV of about 15.4 dl/g. Notethat the curve designated as a “Commercial Sample” had a similar SECcurve as that of the Supported Titanium Catalyst System sample. Thesample also was analyzed by NMR techniques for 1-hexene content.1-Hexene was present in the copolymer in 0.32 mole percent, or expressedin a different manner, in 0.95 weight percent.

[0072] While this invention has been described in detail for the purposeof illustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

That which is claimed is:
 1. A loop/slurry polymerization processcomprising contacting in a reaction zone, at a temperature within arange of about 150° F. to about 180° F. in the presence of a hydrocarbondiluent having three or four carbon molecules per molecule, and in theabsence of hydrogen: a) ethylene monomer; b) higher alpha-olefincomonomer selected from the group consisting of 1-butene, 1-hexene andmixtures thereof; c) a catalyst system comprising a magnesium compoundand a titanium halide, wherein both the magnesium compound and thetitanium halide are supported on an inorganic oxide support and saidcatalyst system has a particle size within a range of about 1 to about40 microns; and d) an aluminum alkyl cocatalyst; and recovering acopolymer of ethylene.
 2. A process according to claim 1 wherein saidreaction zone temperature is within a range of about 160° F. to about170° F.
 3. A process according to claim 1 wherein said inorganic oxidesupport is selected from the group consisting of silica, silica-alumina,alumina, fluorided alumina, silated alumina, thoria, aluminophosphate,aluminum phosphate, phosphated silica, phosphated alumina,silica-titania, coprecipitated silica/titania, fluorided/silatedalumina, and mixtures thereof.
 4. A process according to claim 3 whereinsaid inorganic oxide is a silica-containing support selected from thegroup consisting of silica, silica-alumina, phosphated silica,silica-titania, coprecipitated silica/titania, fluorided/silatedalumina, and mixtures thereof.
 5. A process according to claim 4 whereinsaid support is essentially silica.
 6. A process according to claim 1wherein said catalyst system particle size is within a range of about 2to about 20 microns.
 7. A process according to claim 6 wherein saidcatalyst system particle size is within a range of about 4 to about 16microns.
 8. A process according to claim 1 wherein said aluminum alkylcocatalyst has the general formulae AlR₃, AlR₂X, and/or AlRX₂, wherein Ris an alkyl group having from about 1 to about 12 carbon atoms permolecule and X is a halogen atom.
 9. A process according to claim 9wherein said aluminum alkyl cocatalyst is selected from the groupconsisting of triethyl aluminum, triisobutylaluminum chloride, diethylaluminum chloride, ethylaluminum sesquichloride, and mixtures thereof.10. A process according to claim 9 wherein said aluminum alkylcocatalyst is selected from the group consisting of triethyl aluminum,triisobutyl aluminum and mixtures thereof.
 11. A process according toclaim 1 wherein said aluminum alkyl cocatalyst is present in the reactorin an amount within a range of about 5 to about 500 mg/kg, based on themass of reactor diluent.
 12. A process according to claim 1 wherein saidcatalyst system and aluminum alkyl cocatalyst are contacted prior tocontacting said ethylene.
 13. A process according to claim 1 whereinsaid diluent is isobutane.
 14. A process according to claim 1 whereinsaid copolymer of ethylene comprises a polymer having: a) a weightaverage molecular weight greater than about one million; b) an inherentviscosity greater than about 19; c) a particle size less than about 400microns; c) a density within a range of about 0.92 g/cc to about 0.94g/cc; d) a high load melt index within a range of 0 g/10 minutes; e)about 0.05 to about 3 weight percent comonomer; and e) a sand wheelabrasion loss of less than a about 150 grams.
 15. A copolymer ofethylene according to claim 14 having a weight average molecular weightgreater than about two million.
 16. A copolymer of ethylene according toclaim 14 having an inherent viscosity within a range of about 20 toabout
 28. 17. A copolymer of ethylene according to claim 14 having aparticle size within a range of about 400 microns to about 40 microns.18. A loop/slurry polymerization process comprising contacting in areaction zone, at a temperature within a range of about 150° F. to about180° F. in the presence of a hydrocarbon diluent having three or fourcarbon molecules per molecule, and in the absence of hydrogen: a)ethylene monomer; b) a catalyst system comprising an organometalliccompound selected from the group consisting of zirconium complexed witha beta-stable ligand and hafnium complexed with a beta-stable ligand,wherein the organometallic compound is supported on an inorganic oxidesupport comprising alumina and said catalyst system has a particle sizewithin a range of about 1 to about 40 microns; and c) an aluminum alkylcocatalyst; and recovering a homopolymer of ethylene.
 19. A loop/slurrypolymerization process comprising contacting in a reaction zone, at atemperature within a range of about 150° F. to about 180° F. in thepresence of a hydrocarbon diluent having three or four carbon moleculesper molecule, and in the absence of hydrogen: a) ethylene monomer, b) ahigher alpha-olefin comonomer having from about three to about tencarbon atoms per molecule; c) a catalyst system comprising anorganometallic compound selected from the group consisting of zirconiumcomplexed with a beta-stable ligand and hafnium complexed with abeta-stable ligand, wherein the organometallic compound is supported onan inorganic oxide support comprising alumina and said catalyst systemhas a particle size within a range of about 1 to about 40 microns; andc) an aluminum alkyl cocatalyst; and recovering a copolymer of ethylene.